Welding machine

ABSTRACT

The inventive system and method allows the control of shielding gas in an electric welding apparatus having automatic wire feed by controlling the flow rate of the shielding gas as a function of the wire feeding speed and/or the welding current obtained. A control circuit  112  receives an input signal  203  that is representative for the wire feeding speed and/or the welding current, and issues, in response to the input signal  203 , a control signal  206  to a controllable flow control valve  110  in a gas supply line  201, 202, 208 , which passes shielding gas from a tank  101 , via a regulator valve  102 , to a discharge nozzle of the welding apparatus welding gun. An adjusting unit  113  provides an operator with an interface which permits adjustment of the parameters that determine the flow rate function.

FIELD OF INVENTION

The invention relates to systems for the supply of shielding gas to anarea in which a welding operation is being carried out, and relates inparticular to a control solution which provides control of the shieldinggas supply as a function of the actual welding operation.

BACKGROUND

For welding operations in which the actual welding area is to be coveredwith an inert shielding gas, it is usual to obtain the shielding gasfrom a supply unit where the gas is at a relatively high pressure. It istherefore usual to install a regulator valve in the supply line infairly close proximity to the point at which the actual weldingapparatus is located, and to control the flow rate by means of a flowvalve which is normally fitted on the supply line immediately after theregulator valve. When a wire welding apparatus is used, the weldingapparatus will also be equipped with a simple on/off gas supply valvewhich admits the flow of shielding gas to the welding gun when anoperator starts a welding operation, and shuts off the flow of gas tothe welding gun when the operator finishes the welding operation.Adjustment of the flow rate is usually made by manual adjustment of theflow valve, and will depend upon a number of factors that are associatedwith the welding work to be done. These factors may, for example, be thecharacter of the welding wire, the geometry of the welding gun nozzleand/or the welding current the operator is going to use. To achieve acompleted welding job of a particular quality, it is of utmostimportance that the operator should make the correct adjustment of theregulator valve, and even more important is the correct adjustment ofthe flow valve. A typical system that is used at present is shown inFIG. 1 of the attached drawings.

As can be seen from FIG. 1, a first length of supply line will typicallybe located between the gas tank (or gas supply unit) and the point atwhich the regulator valve and flow valve are located. A second (in thisinstance substantial) length of supply line will be located between thepoint at which the regulator valve and the flow valve are located andthe position of the gas supply valve (which typically is an integralpart of the main unit of the welding apparatus), whilst a third lengthof supply line will be located between the gas supply valve and theactual welding gun nozzle from where the gas can exit freely in order toflow out over the weld. From this it follows that both before the startof a welding operation and after the completion of a welding operation,an “overpressure” will build up in the second length of the supply line,which “overpressure” corresponds to the pressure set in the regulatorvalve. When a welding operation is commenced and the gas supply valveopens, this “overpressure” will result in an immediate and forcefulemission of gas which, after the “overpressure” has been relieved, willtake on a flow rate that is determined by the setting of the flow valve.When the operator has to carry out his welding in the form of manywelding operations of short duration, this results in frequent“blow-outs” which cause both a substantial increase in gas consumptionand undesirable flow conditions at the gas outlet of the welding gunnozzle.

Another factor that is of importance for the quality of a welding job isthat the flow rate is set correctly in relation to other weldingparameters, as mentioned above. Whilst carrying out a welding operation,a welding operator will typically make in-process adjustments ofsettings that affect the feeding speed of the welding wire and/or thevalue of the welding current. When these parameters are changed,corresponding changes should be made in the shielding gas flow rate. Inpractice, changes of the shielding gas flow rate are rarely made, partlybecause the controls for the adjustment of the welding wire feedingspeed and/or the welding current are typically located on the main partof the welding apparatus, which in the case of large welding units areoften located some distance from the position of the flow valve, andpartly because this means yet another operation for the operator. Theoperator may then for his own convenience first set the flow rate whichin any case is high enough to meet all needs, and this in turn mayresult in the use of an unnecessarily high flow rate and thus an“over-consumption” of the expensive shielding gas.

Patent documents DE 3544280, EP 2860974, U.S. Pat. No. 3,811,027, U.S.Pat. No. 4,278,864, U.S. Pat. No. 5,017,757 and U.S. Pat. No. 5,772,102all concern techniques that are related to electric welding, and to avarying degree all deal with the problems concerning shielding gas.However, none of these documents seem to disclose the features thatcharacterise the present invention or to address the aforementionedmatters by providing a solution that corresponds to any of the solutionsof the present invention.

On the basis of the matters mentioned above, there is a need for asolution that will, without any input from the operator, adjust the flowrate of the shielding gas continuously during the performance of awelding job, and control the flow rate of the shielding gas, therebyreducing the total gas consumption.

Accordingly, the object of the invention is to provide solutions wherebyimprovements of the control of the shielding gas supply in a weldingapparatus are obtained.

SUMMARY

The invention provides a control system for controlling the shieldinggas supply to a wire welding apparatus, which wire welding apparatus hasa wire feed device (106) having a feed signal output which is indicativeof a wire feeding speed (U), which wire welding apparatus is connectedto a gas tank (101) via a gas supply line (210, 202), in which supplyline there may according to choice be arranged a pressure regulator(102) and a manometer (103), which is characterised in that the controlsystem comprises a controllable gas flow valve (110) having a valveinlet, a valve outlet and a valve control signal input, a gas flowsensor (111) having a gas inlet, a gas outlet and a sensor signaloutput, and a programmable control circuit (112) having a first and asecond input and a first output, wherein the gas tank has an inletconnection (201, 202) to the valve inlet, the valve outlet has a valveoutlet connection (207) to the gas inlet, the gas outlet has a gasoutlet connection (208) to a shielding gas outlet, the feed signaloutput has a feed signal connection (203) to the first input, the sensorsignal output has a sensor signal connection (205) to the second input,the control signal output has a control signal connection (206) to thevalve control signal input, and the programmable control circuitcomprises a processor which, in accordance with at least one program ina first memory in the control circuit, and on the basis of signalsreceived at the first and second inputs, provides at the first output avalve control signal (Q), which valve control signal has a dynamic rangeof values limited by a predetermined minimum value (Qmin) and apredetermined maximum value (Qmax).

In one embodiment of the invention, a control system is provided asdisclosed above, which is characterised in that the programmable controlcircuit has a third input, which third input is a communications portfor the transfer of the at least one program from a programming device(113), via a communication connection (204), to the memory.

In one embodiment of the invention, a control system is provided asdisclosed above, which is characterised in that the program comprises atleast one instruction to the processor instructing the processor toissue the valve control signal as a signal that is proportional to asignal representing the difference between the signal at the first inputand the signal at the second input.

In one embodiment of the invention, a control system is provided asdisclosed above, which is characterised in that the program comprises atleast one instruction to the processor instructing the processor toissue the valve control signal as a signal that is proportional to asignal representing the difference between the signal at the first inputand the signal at the second input, proportional to a signalrepresenting a time integral of the difference between the signal at thefirst input and the signal at the second input, and proportional to asignal representing a time derivative of the difference between thesignal at the first input and the signal at the second input.

In one embodiment of the invention, a control system is provided asdisclosed above, which is characterised in that the program comprises atleast one instruction to the processor instructing the processor, fromthe time the signal at the first input exceeds a first threshold value(Uth1) and in an immediately subsequent first predetermined time period,to issue at the first output a single signal that is constant and havinga value which corresponds substantially to the minimum value (Qmin).

In one embodiment of the invention, a control system is provided asdisclosed above, which is characterised in that the control circuitcomprises a second memory arranged to continuously register the signalvalue at the first output, and that the program comprises at least oneinstruction to the processor instructing the processor, from the timethe signal at the first input falls short of a second threshold value(Uth2) and in an immediately subsequent second predetermined timeperiod, to issue at the first output a single signal that is constantand having a value that substantially corresponds to the signal value atthe time, or immediately prior to the time, when the signal at the firstinput fell short of the second threshold value.

In one embodiment of the invention, a control system is provided asdisclosed above, which is characterised in that the first thresholdvalue (Uth1) is equal to the second threshold value (Uth2).

In one embodiment of the invention, a control system is provided asdisclosed above, which is characterised in that the control circuitcomprises a control parameter register for storing at least one of theminimum value (Qmin), the maximum value (Qmax), the first thresholdvalue (Uth1), the second threshold value (Uth2), a wire feeding speedminimum threshold (Umin) and a wire feeding speed maximum threshold(Umax); that the program comprises at least one instruction to theprocessor instructing the processor to set the proportionality so thatthe control circuit at the first output issues the minimum value (Qmin)when the wire feeding speed (U) corresponds to the wire feeding speedminimum threshold (Umin) and the maximum value (Qmax) when the wirefeeding speed (U) corresponds to the wire feeding speed maximumthreshold (Umax); and

that the program comprises at least one instruction to the processorinstructing the processor to issue at the first output the minimum value(Qmin) when the wire feeding speed (U) is below the wire feeding speedminimum threshold (Umin) and the maximum value (Qmax) when the wirefeeding speed (U) is above the wire feeding speed maximum threshold(Umax).

In one embodiment of the invention, a control system is provided asdisclosed above, which is characterised in that the programmable controlcircuit has a second output, which second output issues a warning signalwhen the first output issues the minimum value (Qmin), or when the wirefeeding speed (U) is equal to or lower than the wire feeding speedminimum threshold (Umin).

In one embodiment of the invention, a control system is provided asdisclosed above, which is characterised in that the programmable controlcircuit has a second output, which second output issues a warning signalwhen the first output issues the maximum value (Qmax) or when the wirefeeding speed (U) is equal to or higher than the wire feeding speedmaximum threshold (Umax).

In one embodiment of the invention, a control system is provided asdisclosed above, which is characterised in that the communications portis also arranged for the transfer of control parameters from theprogramming device (113), via the communication connection (204), to theprogrammable control circuit.

In one embodiment of the invention, a control system is provided asdisclosed above, which is characterised in that the communications portis also arranged for the transfer between the programming device and theprogrammable control circuit of data stored in, or for storage in, theparameter register and of data representing at least one of a valvecontrol signal (Q), a wire feeding speed (U), and a warning signal.

In one embodiment of the invention, a control system is provided asdisclosed above, which is characterised in that the programming devicecomprises a user interface for the input of control parameters and forthe display of data transferred to and from the programmable controlcircuit.

In one embodiment of the invention, a control system is provided asdisclosed above, which is characterised in that the programming deviceis a personal computer (PC).

The invention provides a method for controlling shielding gas supply toa wire welding apparatus connected to a gas tank (101) via a gas supplyline (210, 202), in which supply line there may according to choice bearranged a pressure regulator (102) and a manometer (103), which wirewelding apparatus comprises a wire feed device (106) having a feedsignal output which is indicative of a wire feeding speed (U), acontrollable gas flow valve (110) having a valve inlet, a valve outletand a valve control signal input, a gas flow sensor (111) having a gasinlet, a gas outlet and a sensor signal output, and a programmablecontrol circuit (112) having a first and a second input and a firstoutput, where the gas tank has an inlet connection (201, 202) to thevalve inlet, the valve outlet has a valve outlet connection (207) to thegas inlet, the gas outlet has a gas outlet connection (208) to ashielding gas outlet, the feed signal output has a feed signalconnection (203) to the first input, the sensor signal output has asensor signal connection (205) to the second input, the control signaloutput has a control signal connection (206) to the valve control signalinput, and the programmable control circuit comprises a processor which,in accordance with at least one program in a first memory in the controlcircuit, and on the basis of signals received at the first and secondinputs, provides at the first output a valve control signal (Q), whichvalve control signal has a dynamic range of values limited by apredetermined minimum value (Qmin) and a predetermined maximum value(Qmax), which is characterised by issuing the valve control signal inthe form of a signal that is proportional to a signal representing thedifference between the signal at the first input and the signal at thesecond input.

The invention provides a method for controlling shielding gas supply toa wire welding apparatus connected to a gas tank (101) via a gas supplyline (210, 202), in which supply line there may according to choice bearranged a pressure regulator (102) and a manometer (103), which wirewelding apparatus comprises a wire feed device (106) having a feedsignal output which is indicative of a wire feeding speed (U), acontrollable gas flow valve (110) having a valve inlet, a valve outletand a valve control signal input, a gas flow sensor (111) having a gasinlet, a gas outlet and a sensor signal output, and a programmablecontrol circuit (112) having a first and a second input and a firstoutput, where the gas tank has an inlet connection (201, 202) to thevalve inlet, the valve outlet has a valve outlet connection (207) to thegas inlet, the gas outlet has a gas outlet connection (208) to ashielding gas outlet, the feed signal output has a feed signalconnection (203) to the first input, the sensor signal output has asensor signal connection (205) to the second input, the control signaloutput has a control signal connection (206) to the valve control signalinput, and the programmable control circuit comprises a processor which,in accordance with at least one program in a first memory in the controlcircuit, and on the basis of signals received at the first and secondinputs, provides at the first output a valve control signal (Q), whichvalve control signal has a dynamic range of values limited by apredetermined minimum value (Qmin) and a predetermined maximum value(Qmax), which is characterised by issuing the valve control signal inthe form of a signal that is proportional to a signal representing thedifference between the signal at the first input and the signal at thesecond input, proportional to a signal representing a time integral ofthe difference between the signal at the first input and the signal atthe second input, and proportional to a signal representing a timederivative of the difference between the signal at the first input andthe signal at the second input.

In one embodiment of the invention, a method is provided as disclosedabove, which is characterised by issuing at the first output, from thetime the signal at the first input exceeds a first threshold value(Uth1) and in an immediately subsequent first predetermined time period,a single signal that is constant and having a value which correspondssubstantially to the minimum value (Qmin).

In one embodiment of the invention, a method is provided as disclosedabove, which is characterised by issuing at the first output, from thetime the signal at the first input falls short of a second thresholdvalue (Uth2) and in an immediately subsequent second predetermined timeperiod, a single signal that is constant and having a value thatsubstantially corresponds to the signal value at the time, orimmediately prior to the time, when the signal at the first input fellshort of the second threshold value.

In one embodiment of the invention, a method is provided as disclosedabove, which is characterised in that the first threshold value (Uth1)is equal to the second threshold value (Uth2).

In one embodiment of the invention, a method is provided as disclosedabove, which is characterised by storing in a control parameter registerin the control circuit at least one of the minimum value (Qmin), themaximum value (Qmax), the first threshold value (Uth1), the secondthreshold value (Uth2), a wire feeding speed minimum threshold (Umin)and a wire feeding speed maximum threshold (Umax); setting theproportionality so that the control circuit at the first output issuesthe minimum value (Qmin) when the wire feeding speed (U) corresponds tothe wire feeding speed minimum threshold (Umin) and the maximum value(Qmax) when the wire feeding speed (U) corresponds to the wire feedingspeed maximum threshold (Umax); and issuing at the first output theminimum value (Qmin) when the wire feeding speed (U) is below the wirefeeding speed minimum threshold (Umin) and the maximum value (Qmax) whenthe wire feeding speed (U) is above the wire feeding speed maximumthreshold (Umax).

In one embodiment of the invention, a method is provided as disclosedabove, which is characterised by issuing at a second output of theprogrammable control circuit a warning signal when the first outputissues the minimum value (Qmin) or when the wire feeding speed (U) isequal to or lower than the wire feeding speed minimum threshold (Umin),or a warning signal when the first output issues the maximum value(Qmax) or when the wire feeding speed (U) is equal to or higher than thewire feeding speed maximum threshold (Umax).

In one embodiment of the invention, a method is provided as disclosedabove, which is characterised by transferring control parameters from aprogramming device (113), via a communication connection (204), to theprogrammable control circuit.

In one embodiment of the invention, a method is provided as disclosedabove, which is characterised by transferring between a programmingdevice (113) and the programmable control circuit, via a communicationconnection (204), data stored in, or for storage in, the parameterregister, and data representing at least one of a valve control signal(Q), a wire feeding speed (U), and a warning signal.

In one embodiment of the invention, a method is provided as disclosedabove, which is characterised by entering control parameters and bydisplaying data transferred to and from the programmable controlcircuit, by means of a user interface in the programming device.

In one embodiment of the invention, a method is provided as disclosedabove, which is characterised in that the programming device is apersonal computer (PC).

The invention also provides a welding apparatus, which is characterisedin that it comprises a control system according to the inventive controlsystem and embodiments thereof as disclosed above.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be explained in more detail with theaid of the attached drawings, wherein:

FIG. 1 is a block drawing schematically illustrating a typical knownshielding gas delivery system;

FIG. 2 is a block drawing schematically illustrating a first embodimentof a shielding gas delivery system which comprises the presentinvention;

FIG. 3 is a block drawing schematically illustrating a second embodimentof a shielding gas delivery system which comprises the presentinvention;

FIG. 4 is a graph illustrating a time sequence example for controlsignals and shielding gas flow rate in a shielding gas delivery systemwhich comprises the present invention;

FIG. 5 is a rough illustration of a possible embodiment of the controlunit according to the second embodiment shown in FIG. 3, forincorporation into the main unit of a wire welding apparatus for controlof the shielding gas flow rate in a shielding gas delivery system whichcomprises the present invention;

FIG. 6 is an illustration of a user interface when a personal computeris used to set different control parameters for a possible embodiment ofa processor-equipped control unit for control of the shielding gas flowrate in a shielding gas delivery system which comprises the presentinvention; and

FIG. 7 is a circuit diagram for the electronic part of a possibleembodiment of a processor-equipped control unit for control of theshielding gas flow rate in a shielding gas delivery system whichcomprises the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A typical known solution for a shielding gas delivery system in an arcwelding apparatus with automatic wire feed is shown in FIG. 1. Thesystem may be formed of a gas tank 101, a tank line 201, a pressureregulator 102 which lowers the pressure to a pressure that is suitablefor further distribution of the gas, a distribution line 202 with amanometer 103, a manually adjustable flow control valve 104 fordetermining the flow rate, a supply line 207 that passes the shieldinggas to the inlet of a gas supply valve 105 in the main unit of thewelding apparatus, which is indicated in a broken line, and a feed line208 which passes the shielding gas from the outlet of the gas supplyvalve 105 to the nozzle of the welding gun, from where the shielding gascan exit freely to the weld. The gas supply valve 105 is typically asolenoid valve with an open position and a closed position, which iscontrolled by an electric signal, which signal also starts or stops themotor that feeds the welding wire, and/or switches the welding currenton or off. This dependence is indicated by the connection 203 from thewire feed motor 106 to the gas supply valve 105. From the illustrationin FIG. 1, it can be seen that when the gas supply valve 105 is closed,gas will flow from the line 202 to the line 207 until the pressure inthe two lines is equal. When the gas supply valve 105 is opened,accumulated gas in the line 207 will flow out in a forceful spurt untilthe pressure difference between the two lines is sufficient for the flowvalve 104 to provide a uniform gas flow.

A first embodiment of the shielding gas delivery system according to theinvention is shown in a block diagram in FIG. 2. The part of the gassupply system that is not associated with the welding apparatus consistsof the gas tank 101, the tank line 201, the pressure regulator 102, andthe distribution line 202 with the manometer 103, whilst the part of thesystem that is associated with the welding apparatus includes acontrollable flow control valve 110, a control unit 112 that has acontrol connection 206 to the flow control valve 110 and connections tothe wire feed motor or its control circuit, and/or to a welding currentcontrol circuit. The control unit 112 is also provided with an inputconnection 204 for connection to an adjusting device 113 for theadjustment of different control parameters. The control unit 112 reactsto a varying input signal at the input connection 204 by issuing anoutput signal at the control connection 206 which varies as a functionof the input signal. In its simplest form, the output signal varies indirect ratio to the input signal, which gives the result that the gasflow rate in the line 208 will vary in direct ratio to the input signal,although within the limits that are obtainable in view of the largestand smallest capacities of the different lines and the valves, and thesetting of the pressure regulator 102. The proportionality factor may beset by means of the adjusting device 113, which for amicroprocessor-based control unit 112 typically will be a data terminal,a personal computer or a similar device. The solution shown in FIG. 2requires a relatively good repeatability in the relation between theoutput signal at the control connection 206 and the gas flow rate thatis actually obtained in the feed line 208, which, among other factors,will be dependent upon the setting of the pressure regulator 102.However, a solution of this kind, especially if formed of low-costcomponents, will require relatively frequent calibration and checking.

It has been found in practice that some controllable flow control valvesover time give great variations in the flow rate, chiefly as aconsequence of pressure variations, temperature and wear.

With reference to the block-diagram presentation in FIG. 3, there willnow follow a description of a second embodiment of a shielding gasdelivery system according to the invention, which gives a betterperformance as regards repeatability and accuracy of the flow rate inthe feed line 208. Broadly, the solution comprises the same solution asdescribed above with reference to FIG. 2, but comprises in addition aflow sensor 11 that is installed in the gas supply line between thecontrollable flow control valve 110 and the feed line 208. The flowsensor 111 has a signal output which issues a signal that is indicativeof the gas flow which at any given time flows through the flow sensor111. The signal output of the flow sensor 111 is connected via theconnection 205 to a corresponding signal input on the control unit 112,so that a feedback loop is formed via the connection 206, thecontrollable flow control valve 110 and the connection 207 to the flowsensor 111. This requires that the flow sensor 111 has sufficientaccuracy and repeatability. In a simple embodiment of the control unit112 in this constellation, a control signal is issued at the connection206 which consists of a signal that is proportional to the input signalat the connection 203 with the addition of a correction signal thatresults from the difference between a first signal derived from thesignal at the connection 203 and a second signal derived from the signalat the connection 205. However, the correction signal may also begenerated by means of a PID (Proportional, Integrating and Deriving)controller in the control unit 112 in order to obtain a rapid response,good stability and high follow-up accuracy. Thus, it is assured that theactual gas flow in the line 208 at all times and without significantdeviations follows a predetermined proportionality factor of the inputsignal at the connection 203. This solution also eliminates the need forfrequent checking and calibration.

In the two embodiments described above with reference to FIGS. 2 and 3,the input signal at the connection 203 represents a varying signal thatis representative for the actual wire feeding speed and/or the weldingcurrent prevailing at any given time. In practice, the main unit of awelding apparatus may comprise an electric direct-current motor thatassures the wire feed, and the voltage supplied to the motor willtherefore be representative of the wire feeding speed and could be useddirectly as the input signal at the connection 203 to the control unit112. In typical electric welding apparatus, there will be dependencebetween wire feeding speed and welding current, and for apparatus ofthis kind it is not important for the invention whether the operator'sadjustments of the apparatus during the performance of a welding job aremade to the wire feeding speed or to the welding current.

With reference to the graph in FIG. 4, there will now be described bymeans of an example a gas flow course in a shielding gas supply systemaccording to the invention during the performance of a welding job wherethe operator makes adjustments to the wire feeding speed (or the weldingcurrent) during the performance of a welding operation. U indicatesdirect current, illustrated in a broken line, which is supplied to awire feed motor and which determines the wire feeding speed, whilst Qindicates the gas flow, illustrated in a solid line, which flows in thefeed line to the welding gun nozzle. At time 301, the operator depressesthe trigger switch on the welding gun, which results in voltage beingsupplied to the wire feed motor. The motor voltage, and speed, increaserapidly and at the time 302 pass a first threshold Uth at which thecontrol unit 112 is activated. When activated, the control unit 112issues a constant control signal which indicates a constant minimum flowrate during a time period T1. At the time 303, which is at the end ofthe time period T1, the control unit 112 issues a control signal to theflow control valve 110 which assures a gas flow that variesproportionally to the control signal, i.e., proportionally to the motorvoltage, and thus also proportionally to the wire feeding speed.However, the operator has set a maximum flow rate Qmax that should becoincident with a maximum voltage Umax, and a minimum flow rate Qminwhich should be coincident with a minimum voltage Umin. As the operatoradjusts the wire feeding speed during the welding operation, the motorvoltage U exceeds the maximum voltage Umax at the time 304, and the flowrate Q of the gas is therefore maintained constant at Qmax until thetime 305 when the motor voltage has again been adjusted to a value thatis less than Umax. From the time 305, the flow rate Q of the gas againvaries proportionally to the feeding speed (represented by U), as set bythe operator, until the operator, at the time 306, releases the triggeron the welding gun, with the result that the motor voltage U dropsquickly and falls below the threshold voltage Uth at the time 307. Thecontrol unit 112 registers that the voltage U falls below the thresholdUth, and will at the time 307, depending on the parameter settings ofthe control unit 112, either assure the immediate shut-off of the gasflow by deactivation of the control unit 112, or by means of a memory inthe control unit 112 maintain the gas flow at a flow rate Q, whichcorresponds to the rate that was present at the time 306, for a timeperiod T2 until the time 308, whereupon the control unit 112 isdeactivated.

With reference to FIG. 6, seen in conjunction with FIG. 5, there isshown an example of a user interface in connection with the adjustingdevice consisting of a personal computer. With reference to theexplanation of FIG. 5 above, the reader will again recognise thepossible adjustments for the maximum voltage Umax, the minimum voltageUmin, the threshold voltage Uth, the maximum flow rate Qmax, the minimumflow rate Qmin, the start pulse time period T1 and the stop pulse timeperiod T2. By comparing FIGS. 5 and 6, it will be seen that for theillustrated example in FIG. 4, the proportionality factor between theinput signal (wire feeding speed) at the connection 203 and the controlsignal (flow rate) at the connection 206 is determined by the settingsfor Umin and Qmin, and Umax and Qmax.

Although the invention has been explained with all settings for Umin,Umax, Uth, Qmin, Qmax, T1 and T2 set as values that make them activeduring the performance of the welding operation example explained above,the invention can also be carried out in such manner that one or more ofthese parameters may be omitted. For example, it is conceivable thatsome welding apparatus will never be used to perform welding operationswhich make it necessary to use an “afterflow” of gas during a timeperiod T2, in which case this control parameter can be completelyomitted, both as functionality in the control unit 112, and in theinterface in an adjusting means 113.

More generally, the relation between the input signal (wire feedingspeed, or welding current) to and the control signal (the flow rate)from the control unit 112 is described by the expression:Q=f(U).

Thus, the relation between input signal and control signal does not needto be proportional or linear, as there could be other important factorsfor the welding job which may require another dependence. By using amicroprocessor, or a microcontroller, in the control unit 112, theimplementation of the majority of conceivable relations will be to solverelatively simple program-technical tasks.

The control unit 112 can also be provided with both standard settingsand tables for other settings and parameters, depending upon factorssuch as the wire type used, the material to be welded, gas type, ambientconditions and so forth. Through a logically constructed interface, theoperator will easily be able to reset both the apparatus and theshielding gas supply, which in turn will mean better economy and agreater certainty that the result of a welding operation has the desiredquality.

In one embodiment of a shielding gas delivery system according to theinvention, the flow control valve 111 consists of an electric pulsedvalve means. The control signal to the flow control valve 111 will inthis case be a pulse train with varying frequency and/or pulse factor asa function of the input signals to the control unit 112.

In FIGS. 2 and 3, the control unit 112 is provided with an outputconnection 209. This is an optional output connection which could carryone or more warning or indicator signals that may be useful during theperformance of a welding operation. For example, the control unit 112may issue a warning signal that tells the operator that the flow ratehas reached the maximum value Qmax, or for example, in the case of theconstellation in FIG. 2, that the correction signal derived from thesignal from the flow sensor 111 is not capable of correcting adeviation, with the result that the flow rate will deviate from thedesired value. The last-mentioned case could occur, for example if thegas tank runs empty during the performance of a welding operation.

Although the invention has been explained using examples thatessentially use electric signals between the different elements, theinvention could be realised using other types of signals carriers, asfor instance by using pneumatic, hydraulic, optical or mechanical meansfor signal transmission. Optionally, a combination of different signalscould be used, as for instance an electric input signal to the controlunit 112 at the connection 203, and a pneumatic control signal from thecontrol unit 112 to the flow control valve 110 at the connection 206.

1. A control system for controlling the shielding gas supply of anautomatic welding apparatus, which automatic welding apparatus has acontinuous electrode feed device having a feed signal output which isindicative of a continuous electrode feeding speed (U), which automaticwelding apparatus is connected to a gas tank via a gas supply line, inwhich supply line there may according to choice be arranged a pressureregulator and a manometer characterised in that the control systemcomprises a controllable gas flow valve having a valve gas inlet, avalve gas outlet and a valve control signal input for receiving a valvecontrol signal; a gas flow sensor having a gas inlet, a gas outlet and asensor signal output; and a programmable control circuit having a firstand a second input and a first output; wherein the gas tank has an inletconnection to the valve gas inlet, the valve gas outlet has a valveoutlet connection to the gas inlet, the gas outlet has a gas outletconnection to a shielding gas outlet, the feed signal output has a feedsignal connection to the first input, the sensor signal output has asensor signal connection to the second input, the first output has acontrol signal connection to the valve control signal input, theprogrammable control circuit comprises a processor which, in accordancewith at least one program in a first memory in the control circuit, andon the basis of signals received at the first and second inputs,provides at the first output the valve control signal, which providedvalve control signal is adjustable by means of the programmable controlcircuit within a dynamic range of values limited in accordance with apredetermined minimum gas flow (Qmin) through the valve and apredetermined maximum gas flow (Qmax) through the valve, and the programcomprises at least one instruction to the processor instructing theprocessor to issue at the first output a signal that is constant andhaving a value which corresponds substantially to the minimum gas flow(Qmin) through the valve from the time the signal at the first inputexceeds a first threshold value (Uth1) and in an immediately subsequentfirst predetermined time period.
 2. The control system of claim 1,characterised in that the programmable control circuit has a thirdinput, said third input is a communications port for the transfer of theat least one program from a programming device, via a communicationconnection, to the memory.
 3. The control system of claim 2,characterised in that the first threshold value (Uth1) is equal to asecond threshold value (Uth2).
 4. The control system of claim 2,characterised in that the communications port is also arranged for thetransfer of control parameters from the programming device, via thecommunication connection, to the programmable control circuit.
 5. Thecontrol system of claim 2, characterised in that the communications portis also arranged for the transfer between the programming device and theprogrammable control circuit of data stored in, or for storage in, theparameter register and of data representing at least one of a valvecontrol signal, a feeding speed (U), and a warning signal.
 6. Thecontrol system of claim 2, characterised in that the programming devicecomprises a user interface for the input of control parameters and forthe display of data transferred to and from the programmable controlcircuit.
 7. The control system of claim 2 characterised in that theprogramming device is a personal computer (PC).
 8. The control system ofclaim 1, characterised in that the program comprises at least oneinstruction to the processor instructing the processor to issue thevalve control signal as a signal that is proportional to a signalrepresenting the difference between the signal at the first input andthe signal at the second input.
 9. The control system of claim 1,characterised in that the program comprises at least one instruction tothe processor instructing the processor to issue the valve controlsignal as a signal that is proportional to a signal representing thedifference between the signal at the first input and the signal at thesecond input, proportional to a signal representing a time integral ofthe difference between the signal at the first input and the signal atthe second input, and proportional to a signal representing a timederivative of the difference between the signal at the first input andthe signal at the second input.
 10. A method for controlling a shieldinggas supply in an automatic welding apparatus by means of the controlsystem of claim 1, the method characterised by outputting the valvecontrol signal at the first output in the form of a signal that isproportional to a signal representing a difference between the signal atthe first input and the signal at the second input, and outputting atthe first output the valve control signal as a signal that is constantand having a value which corresponds substantially to the minimum gasflow (Qmin) through the valve from the time the signal at the firstinput exceeds a first threshold value (Uth1) and in an immediatelysubsequent first predetermined time period.
 11. A method for controllinga shielding gas supply in an automatic welding apparatus by means of thecontrol system of claim 1, the method characterised by outputting thevalve control signal at the first output in the form of a signal that isproportional to a signal representing the difference between the signalat the first input and the signal at the second input, and outputting atthe first output, from the time that the signal at the first input fallshort of a second threshold value (Uth2) and in an immediatelysubsequent second predetermined time period, the valve control signal asa signal that is constant and having a value that substantiallycorresponds to the signal value at the time, or immediately prior to thetime, when the signal at the first input fell short of the secondthreshold value.
 12. The method of claim 11, characterised in that thefirst threshold value (Uth1) is equal to the second threshold value(Uth2).
 13. The method claim 11, characterised by storing in a controlparameter register in the control circuit at least one of the minimumgas flow (Qmin) through the valve, the maximum gas flow (Qmax) throughthe valve, the first threshold value (Uth1), the second threshold value(Uth2), a continuous electrode feeding speed minimum threshold (Umin)and a continuous electrode feeding speed maximum threshold (Umax);setting a proportionality so that the control circuit at the firstoutput issues the valve control signal in accordance with minimum gasflow (Qmin) through the valve when the continuous electrode feedingspeed (U) corresponds to the wire feeding speed minimum threshold (Umin)and the maximum gas flow (Qmax) through the valve when the wire feedingspeed (U) corresponds to the wire feeding speed maximum threshold(Umax); and by issuing at the first output the valve control signal inaccordance with the minimum gas flow (Qmin) through the valve when thewire feeding speed (U) is below the feeding speed minimum threshold(Umin) and the maximum gas flow (Qmax) through the valve when thefeeding speed (U) is above the feeding speed maximum threshold (Umax).14. The method of claim 11, characterised by issuing at a second outputof the programmable control circuit a warning signal when the firstoutput issues the valve control signal in accordance with the minimumgas flow (Qmin) through the valve or when the feeding speed (U) is equalto or lower than the feeding speed minimum threshold (Umin), or awarning signal when the first output issues the valve control signal inaccordance with the maximum gas flow (Qmax) through the valve or whenthe feeding speed (U) is equal to or higher than the wire feeding speedmaximum threshold (Umax).
 15. The method of claim 11, characterised bytransferring control parameters, from a programming device via acommunication connection to the programmable control circuit.
 16. Themethod, of claim 11 characterised by transferring between a programmingdevice and the programmable control circuit, via a communicationconnection, data stored, or for storage in the parameter register, anddata representing at least one of a valve control signal, a feedingspeed (U), and a warning signal.
 17. The method of claim 16,characterised by entering control parameters and by displaying datatransferred to and from the programmable control circuit, by means of auser interface in the programming device.
 18. The method of claim 16,characterised in that the programming device is a personal computer(PC).
 19. A method for controlling a shielding gas supply in anautomatic welding apparatus by means of the control system of claim 1,the method characterised by outputting the valve control signal at thefirst output in the form of a signal that is proportional to a signalrepresenting the difference between the signal at the first input andthe signal at the second input, proportional to a signal representing atime integral of the difference between the signal at the first inputand the signal at the second input, and proportional to a signalrepresenting a time derivative of the difference between the signal atthe first input and the signal at the second input, and outputting atthe first output the valve control signal as a signal that is constantand having a value which corresponds substantially to the minimum gasflow (Qmin) through the valve from the time that the signal at the firstinput exceeds a first threshold value (Uth1) and in an immediatelysubsequent first predetermined time period.
 20. A method for controllinga shielding gas supply in an automatic welding apparatus by means of thecontrol system of claim 1, the method characterised by outputting thevalve control signal at the first output in the form of a signal that isproportional to a signal representing the difference between the signalet the first input and the signal at the second input, proportional to asignal representing a time integral of the difference between the signalat the first input and the signal at the second input, and proportionalto a signal representing a time derivative of the difference between thesignal at the first input and the signal at the second input, andoutputting at the first output, from the time that the signal at thefirst input falls short of a second threshold value (Uth2) and in aimmediately subsequent second predetermined time period, the valvecontrol signal as a signal that is constant and having a value thatsubstantially corresponds to the signal value at the time, orimmediately prior to the time, when the signal at the first input fellshort of the second threshold value.
 21. A welding apparatus,characterised in that it comprises the control system of claim
 1. 22. Acontrol system for controlling the shielding gas supply of an automaticwelding apparatus, which automatic welding apparatus has a continuouselectrode feed device having a feed signal output which is indicative ofa continuous electrode feeding speed (U), which automatic weldingapparatus is connected to a gas tank via a gas supply line, in whichsupply line there may according to choice be arranged a pressureregulator and a manometer characterised in that the control systemcomprises a controllable gas flow valve having a valve gas inlet, avalve gas outlet and a valve control signal input for receiving a valvecontrol signal; a gas flow sensor having a gas inlet, a gas outlet and asensor signal output; and a programmable control circuit having a firstand a second input and a first output; wherein the gas tank has an inletconnection to the valve gas inlet, the valve gas outlet has a valveoutlet connection to the gas inlet, the gas outlet has a gas outletconnection to a shielding gas outlet, the feed signal output has a feedsignal connection to the first input, the sensor signal output has asensor signal connection to the second input, the first output has acontrol signal connection to the valve control signal input, theprogrammable control circuit comprises a processor which, in accordancewith at least one program in a first memory in the control circuit, andon the basis of signals received at the first and second inputs,provides at the first output the valve control signal, which providedvalve control signal is adjustable by means of the programmable controlcircuit within a dynamic range of values limited in accordance with apredetermined minimum gas flow (Qmin) through the valve and apredetermined maximum gas flow (Qmax) through the valve, and the controlcircuit comprises a second memory arranged to continuously register thesignal value at the first output of the control circuit; and that theprogram comprises at least one instruction to the processor instructingthe processor issue at the first output from the time the signal at thefirst input falls short of a second threshold value (Uth2) and in animmediately subsequent second predetermined time period signal that isconstant and having a value that substantially corresponds to the signalvalue at the time, or immediately prior to the time, when the signal atthe first input fell short of the second threshold value.
 23. Thecontrol system of claim 22, characterised in that the control circuitcomprises a control parameter register for storing at least one of theminimum gas flow (Qmin) through the valve, the maximum gas flow (Qmax)through the valve, a first threshold value (Uth1), the second thresholdvalue (Uth2), a continuous electrode feeding speed minimum threshold(Umin) and a continuous electrode feeding speed maximum threshold(Umax), that the program comprises at least one instruction to theprocessor instructing the processor to set a proportionality so that thecontrol circuit at the first output issues the valve control signal inaccordance with minimum value (Qmin) when the feeding speed (U)corresponds to the feeding speed minimum threshold (Umin) and inaccordance with the maximum value (Qmax) when the feeding speed (U)corresponds to the feeding speed maximum threshold (Umax); and that theprogram comprises at least one instruction to the processor instructingthe processor to issue at the first output the valve control signal inaccordance with the minimum gas flow (Qmin) through the valve when thecontinuous electrode feeding speed (U) is below the feeding speedminimum threshold (Umin) and the valve control signal in accordance withthe maximum gas flow (Qmax) through the valve when the feeding speed (U)is above the feeding speed maximum threshold (Umax).
 24. The controlsystem of claim 23, characterised in that the programmable controlcircuit has a second output that issues a warning signal when the firstoutput issues the valve control signal in accordance with the minimumgas flow (Qmin) through the valve or when the feeding speed (U) is equalto or lower than the feeding speed minimum threshold (Umin).
 25. Thecontrol system of claim 23, characterised in that the programmablecontrol circuit has a second output that issues a warning signal whenthe first output issues the valve control signal in accordance with themaximum gas flow (Qmax) through the valve or when the feeding speed (U)is equal to or higher than the feeding speed maximum threshold (Umax).